1. Field of the Invention
The present invention generally relates to ink jet printhead apparatus and more particularly relates to systems for piezoelectrically driving an ink jet printhead.
2. Description of Related Art
A piezoelectrically actuated ink jet printhead is a relatively small device used to selectively eject tiny ink droplets onto a paper sheet operatively fed through a printer, in which the printhead is incorporated, to thereby form from the ejected ink droplets selected text and/or graphics on the sheet. In one representative configuration thereof, an ink jet printhead has a horizontally spaced parallel array of internal ink-receiving channels. These internal channels are covered at their front ends by a plate member through which a spaced series of small ink discharge orifices are formed. Each channel opens outwardly through a different one of the spaced orifices.
A spaced series of internal piezoelectric wall portions of the printhead body separate and laterally bound the channels along their lengths. To eject an ink droplet through a selected one of the discharge orifices, the two printhead sidewall portions that laterally bound the channel associated with the selected orifice are piezoelectrically deflected into the channel and then returned to their normal undeflected positions. The driven inward deflection of the opposite channel wall portions increases the pressure of the ink within the channel sufficiently to force a small quantity of ink, in droplet form, outwardly through the discharge orifice.
According to a recently proposed drive method for this type of ink jet printhead, top sides of the internal channel dividing wall portions are commonly connected to ground, and the bottom sides of the wall portions are individually connected to a series of electrical actuating leads. Each of these leads, in turn, is connected to a drive control system operable to selectively impart to the lead a wave form that sequentially changes (1) from ground to a first driving polarity, (2) from the first polarity to the opposite polarity, and (3) from the opposite polarity back to ground.
When this electrical wave form is imparted to a piezoelectric wall portion bounding one side of a selected, and a second analog electrical wave form of opposite polarity sequence is simultaneously imparted (via another one of the actuating leads) to the opposite channel wall portion, the opposite channel wall portions, by piezoelectrical action, are sequentially deflected (1) outwardly away from the channel that they laterally bound, (2) into the channel to discharge an ink droplet therefrom, and (3) back to their starting or "neutral" positions.
While the drive system just described provides its printhead with satisfactory printing performance, it has several built-in limitations and disadvantages. For example, the system requires three separate drivers--one for each of the three channel wall drive portions described above. This requirement substantially increases the complexity of the drive system, thereby undesirably increasing its overall cost. Additionally, it undesirably increases the overall space requirement for the drive system.
It can be readily seen from the foregoing that it would be desirable to provide an improved ink jet printhead drive system that eliminates, or at least substantially reduces, the above-mentioned limitations and disadvantages associated with the drive system described above. It is accordingly an object of the present invention to provide such an improved ink jet printhead drive system.